1. Field of the Invention
The present invention relates to a battery cell such as a nonaqueous electrolytic secondary cell in which a winding-type power-generating element is housed within a cell case, and a battery (multiple-cell set) using it.
2. Description of the Related Art
An explanation will be given of a conventional structure of a large-scale large-capacity elliptic-cylindrical nonaqueous secondary cell 1. As seen from FIG. 19, a power generating element 2 of the nonaqueous secondary cell is composed of a belt-shaped electrolytic positive electrode 2a and a belt-shaped negative electrode 2b which are wound in an elliptic-cylinder through belt-shaped separators 2c. The positive electrode 2a has an area of a mixture 2d of an active material and binder for the positive electrode applied on the surface of an aluminum foil and another area on which the mixture 2d is not applied and to which the aluminum foil is exposed at the belt-shaped lower end of the foil. The negative electrode 2b has an area of a mixture 2e of an active material and binder for the negative electrode applied on the surface of a copper foil and another area on which the mixture 2e is not applied and to which the copper foil is exposed at the belt-shaped upper end of the foil. These positive electrode 2a and a negative electrode 2b are wound in a manner displaced horizontally little by little so that the lower end of the positive electrode 2a protrudes downward and the upper end of the negative electrode 2b protrudes upward.
As seen from FIG. 20, a negative electrode collector 9 is fixedly connected to the upper end of the negative electrode 2b of the power generating element 2 which protrudes upwards. The negative electrode collector 9 is made by stamping a copper alloy plate and folded to form slits. The copper foils exposed to the upper ends of the negative electrodes 2b are inserted in and fixedly connected to the respective slits by clamping or welding. A negative electrode terminal 5 of a copper alloy is fixedly connected to the negative electrode collector 9 by clamping or welding so that it protrudes upward. A positive electrode collector 8 is fixedly connected to the lower end of the positive electrode 2a of the power generating element 2 which protrudes downwards. The positive electrode collector 8 is made by stamping an aluminum alloy plate and folded to form slits. The aluminum foils exposed to the lower ends of the positive electrodes 2a are inserted in and fixedly connected to the respective slits by clamping or welding. The one end of the positive electrode collector 8 is extended to the negative electrode collector 9 along the power generating element 2 to reach the upper side thereof. A positive electrode terminal 4 of the aluminum alloy is fixedly connected to the positive electrode collector 8 by clamping or welding.
The power generating element 2 to which the positive electrode collector 8 and the negative electrode collector 9 are connected is housed within a cell case 3 as shown in FIG. 21. The cell case 3 is made of an aluminum alloy plate or stainless steel plate, and is composed of an elliptic-cylindrical vessel-shaped case body 3a and an elliptic cover plate 3b fit in the upper opening thereof and sealed by welding on the periphery. The positive electrode terminal 4 and negative electrode terminal 5 which are fixedly connected to the power generating element 2 are caused to protrude upwards through the opening holes located at two positions of the cover plate 2 from the inside of the cell case 3. These electrode terminals 4 and 5 are electrical insulating sealed by forming a glass hermetic seal in gaps between themselves and the opening holes. Incidentally, a metallic ring made of the same material as the cover plate 3b is electrical insulating secured to each of these positive electrode terminal 4 and negative electrode terminal 5 by a glass. hermetic seal or ceramic hermetic seal. These metallic rings are secured to seal the opening holes at two positions of the cover plate 3b. The cover plate 3b, thereafter, is fit in the case body 3a and sealed therein by welding.
The nonaqueous electrolytic secondary cell 1 is accompanied by the following danger. Namely, when the power generating element 2 is heated excessively while abnormality occurs, the electrolyte is decomposed to generate gas. Then, the inside pressure is boosted so that the cell case 3 may be broken. In order to overcome such an inconvenience, in the conventional art, safety valves 6 were formed on the bottom of the case body 3a and on the cover plate 3b. The safety valves 6 are constructed by the plate areas thinned by forming grooves in the aluminum alloy plate or stainless steel plate constituting the case body 3a and cover plate 3b. When the pressure within the cell case 3 is boosted abnormally, the grooved thin plate areas are broken so that the inside of the cell case is degassed.
Now, it should be noted that the gas generated in the power-generating element 2 can move only toward either the upper end or lower end along a winding axis direction because the positive electrode 2a and negative electrode 2b are closely wound. In order to avoid such an inconvenience, safety valves 6 are formed on the bottom of the case body 3a and on the cover plate 3b so that the gas moved out from the upper and lower ends in the winding axis direction can be smoothly discharged externally. However, where such an elliptic-cylindrical nonaqueous electrolytic secondary cell 1 is used as a single cell, when the internal pressure increases, the planar portion of the side wall of the case body 3a swells outwardly. Therefore, for example, the gas moved out from the lower end of the power-generating element 2 can be transferred to the upper end through the swelled side of the case body 3a. In this case, the safety valve 6 may be formed on only the cover plate 3b at the upper end. However, where a plurality of the nonaqueous electrolytic secondary cells 1 are closely arranged so that they can be used as a battery, the planar portions of the sides of the adjacent nonaqueous electrolytic secondary cells push each other so that each battery cannot swell by the internal pressure unlike the case of the single cell. Thus, the gas moved out from the lower end of the power generating element 2 cannot shift. In this case, the safety valve 6 must be also formed on the bottom of the case body 3a. 
Where the conventional nonaqueous electrolytic secondary cell 1 is used as a constituent of the battery, it cannot be used with the bottom of the cell where the safety valve 6 is formed being closed. For example, in the case of the battery for a special use such as aeronautics/space, as shown in FIG. 22, a cooling plate 7 of a material having a high thermal conductivity such as an aluminum alloy is arranged between the plurality of nonaqueous electrolytic secondary cells 1 and beneath the bottom of each nonaqueous secondary cell so that the battery can be cooled by a cooling means (not shown). In this case, the planar portion of the side of each nonaqueous secondary cell 1 is restrained by the cooling plate 7 and hence cannot swell. This requires for the safety valve to be formed on the bottom of the case body 3a. 
However, because the bottom of the case body 3a is also blocked by the cooling plate 7, the safety valve 6 cannot operate normally.
Even where the nonaqueous electrolytic secondary cell 1 is used as a single cell, if the side wall of the case body 3a cannot swell because the cell is arranged with no gap within an installing space, the safety valve 6 must be formed on the bottom of the case body 3a. In this case also, the cell must be used with the bottom of the cell where the safety valve 6 is formed being not closed.
In the case of the cylindrical nonaqueous electrolytic secondary cell, the entire side wall of the cell case is curved and has no planar portion. Therefore, even where it is arranged within an sufficient installing space as a single cell, the side wall of the cell cannot swell. In this case also, the safety valves must be formed on the upper and lower face of the cell case, and hence the cell cannot be used with the bottom of the cell where the safety valve 6 is formed being closed.
Such a problem applies to not only the nonaqueous electrolytic secondary cell, but also all the batteries which require a safety valve and use a winding type power-generating element.
The present invention has been accomplished in order to solve such a problem, and it is an object of the present invention to provide a battery which is provided with a safety valve on the side wall of a cell case in the vicinity of a bottom thereof so that the cell can be used with the bottom being closed, and a battery using such a cell.
According to the first aspect of the present invention, in a cell in which a winding type power generating element is housed within a cell case, on a side wall of the cell case along a winding axis direction of the power generating element, a safety valve is formed at a position inclusive of the tip end of a mixture-applied area of at least one electrode of the power generating element.
In accordance with the first aspect of the present invention, since the safety valve is formed at at least one end of the side wall of the cell case, even where the one end surface of the battery is closed, the gas moved out from the one end of the winding type power generating element can be smoothly discharged externally. The safety valve may be formed at each of both ends of the side wall of the cell case.
According to the second aspect of the present invention, in a battery in which an elliptic-cylindrical winding type power generating element is housed within an elliptic-cylindrical cell case, on an elliptic-cylindrical curved surface of a side wall of the cell case along a winding axis direction of the power generating element, a safety valve is formed at a position inclusive of the tip end of a mixture-applied area of at least one electrode of the power generating element.
In accordance with the second aspect of the present invention, since the safety valve is formed at the curved portion of the elliptic-cylindrical cell case, even where the planar portion of the side wall is restrained so that it cannot swell, the inner gas can be smoothly discharged horizontally.
According to the third aspect of the present invention, in the battery of the first or second aspect, the height of the cell along its side wall is 1.5 times or more as large as the narrowest width of the cell case.
In accordance with the third aspect of the present invention, since the length of the power generating element in the winding direction along the side wall of the cell case is sufficiently longer than the width thereof, the gas that may not escape at the one side of the cell case if there is no safety valve can be surely discharged externally from the safety valve formed on the side wall.
According to the fourth aspect of the present invention, in a battery, a plurality of the cells defined in any of the first to the third aspect of the present invention are arranged with the tip end located on their bottom side, and a cooling plate is arranged on their bottom side and between adjacent cells.
In accordance with the fourth aspect of the present invention, even where the side and bottom of the cell case of each of the batteries are blocked by the cooling plate of the battery, since the safety valve is formed at the bottom side of the side wall of each cell case, the gas move out from the bottom of the winding type power generating element can be smoothly discharged externally.